The invention relates to a method of making whisker reinforced ceramic tools for shaping or otherwise working materials. The invention has particular application in making metal working tools, and specifically tools used in the manufacture of tubular casings and similar articles, such as two-piece beverage cans.
Tools for imparting a desired shape, form, or finish to a material, such as dies, punches, and the like, must be characterized by extreme hardness, compressive strength and rigidity. This is particularly necessary when shaping metals or similar materials. Commercial material working tools for assembly line mass production must also be resistant to wear, erosion and chipping from repeated and continuous stress, and abrasion. These tools must also be made from materials which can be designed and machined to close tolerances and maintain dimensional stability over a wide range of operating conditions.
It is known to make punches, dies, deep draw tooling and similar material working tools from a variety of materials, including metals, tungsten carbide, and conventional ceramics. These known materials all have certain undesirable limitations. When making tools for shaping metal articles, particularly tubular casings such as two-piece beverage cans, the problems of prior known materials becomes particularly significant.
Beverage cans are generally made either as a three-piece can or a two-piece can. In a conventional three-piece beverage can, an appropriately sized body blank is cut from a large metal plate and bent into a cylindrical tube having a soldered side seam. The ends of the tube are flanged. An end closure member, or lid, is attached to one end of the body. A second end closure member is applied after filling the can. The body and two end closures constitute the three-piece can. For printed cans the metal plate is printed prior to cutting the plate into individually sized body blanks.
A two-piece beverage can has a body having an integrally formed closed end and a single end closure member. A two-piece beverage can is manufactured by a process fundamentally different than that for making a three-piece can. Two-piece cans have been available only since the early 1970s. The present invention provides significant advantages particularly in the manufacture of two-piece beverage cans. However, as will be readily understood from the following description of the invention, the invention has broad applicability for use in manufacturing a variety of shaped articles, particularly tubular casings, such as fountain pens and dry cell battery casings.
A two-piece can is made by a drawing and wall ironing process that results in only two-pieces, a combined body and base and an end closure. In general, a two-piece can is made by stamping out metal discs from a metal plate. A metal "cup" is formed from the disk by holding the disk in a cup-forming die and moving a cup-forming punch through the cup-forming die. The formed cups are then transferred to a body making machine where they are pushed through a body-forming die comprising a plurality of annular rings, generally known as draw, redraw, and ironing rings, by a body-forming punch. The clearances between the body-forming punch and the plurality of rings become progressively smaller, so that the cup walls are ironed out into a thin section. A domer punch will then press the bottom of the can body into a concave configuration for added strength.
After the body is formed, the open end of the can is trimmed to the exact desired length. The can is then washed, dried, and prepared for necking, i.e., the process of forming a neck on the open end. However, before necking, for cans that are to be printed with a label, the can may be transferred to a multi-station printer. The can is placed onto a printer mandrel which brings the can into engagement with a paint roller. After printing the can is moved to a drying oven.
The final step in forming a two-piece can is necking and flanging. These operations prepare the top of the can so that it is ready to receive a lid after being filled. Generally, this is done in a multistage die-necking machine which includes a necker die, for necking-in the open end of the can, and a disc for forming a flange on the necked-in, open end of the can. This disc is generally referred to as a "spinnecker" disc.
Throughout the process of making a two-piece beverage can, various special tooling is required. This tooling must be sufficiently strong, abrasion resistant and inert to produce an acceptable can. In 1986, over 70 billion metal beverage cans were manufactured in the United States. These cans were made on production lines which produce cans at a rate of 1200 to 2000 cans per minute. Ninety-five (95%) percent of those cans were made of aluminum, with the remainder being made of steel. The present invention may be used in the manufacture of both aluminum and steel cans, as well as other metal and nonmetal products.
Because of the tremendous volume of beverage cans manufactured each year, each slight improvement in the manufacturing process can result in tremendous savings. Over the years, for instance, the industry has made every possible effort to reduce the weight of the cans so as to reduce material costs. In 1965, one thousand aluminum beverage cans weighed 51.6 pounds, whereas in 1986 one thousand aluminum beverage cans weighed 27.5 pounds. As technology has advanced, there have also been marked improvements in strength, dimensional consistency, and quality of finish. However, further improvements are still sought.
The most common material for the various tools used in the process of making a two-piece beverage can, including the cup-forming die and cup-forming punch, the body-forming die and body-forming punch, the necker die and the spinnecker disc, is tungsten carbide, usually held in a hardened tool steel body. However, tungsten carbide can-making tools wear considerably and must be replaced or refinished often. Additionally, when making aluminum cans, tungsten carbide tools contribute to the formation of aluminum oxide on the surface of the aluminum cans, which must be removed prior to filling the can with a beverage. Also, particularly in aluminum cans, the commonly used tungsten carbide can-making tools leave scratch marks on the surface of the can body. These scratches create points of stress concentration and significantly reduce the strength of the can sidewall, which generally is only 0.004 inches thick. A more uniform wall thickness results in a greater stacking strength, less collapsing, and less leakage from cans. The scratches also make finishing the inside and outside surfaces of the can more difficult. Because of the lack of a smooth, finished surface significantly more epoxy resin coating must be used to coat the inside of the can. Printing on the outside of the can is also adversely affected.
Tungsten carbide components also generate considerably more heat through friction during the can-making process. The heat resulting from the friction causes a significant variance in the dimensions of the can, including wall thicknesses. To reduce the friction, it is common to use synthetic lubricants. These lubricants, however, require intensive washing of the can to remove the lubricant. This is a difficult, costly and time-consuming step.
The present invention is specifically intended to overcome the deficiencies of tungsten carbide components used in the manufacture of two-piece cans. However, as will be readily understood from the following description, the invention has broad applicability to the manufacture of other articles.